This invention relates generally to an automatic fault detecting and modem bypass circuit for use in connection with a digital data transmission loop system.
Referring to FIG. 1 of the drawings, a typical telephone cable data transmission hub portion of a data transmission loop of the type well known in the prior art is shown. Typically, a controller 10 such as an IBM 3604 which is centrally located as at the main headquarters of a bank or savings and loan institution is connected to a modem 12. The modem 12 performs the input/output or modulate/demodulate function of the data transmission system in a well known manner. Typical systems such as the IBM 3600 employ a controller and modem which supply a carrier signal which can be frequency shift-keyed in a well known manner to transmit digital information about the loop to a plurality of remotely located modems 14. The various modems 14 are series connected with one another through various two-wire modem input and output lines 16 and 18, respectively, which extend to and from a more or less centrally located collecting station 20. A main line 22 consisting of a pair of input and output cables supplies information between the controller 10 and various remotely located and series connected modems 14 by way of the collecting station 20. Within the central collecting station 20, the various modem input and output lines 16 and 18 are series connected through conventional line amplifiers 24. The hub collecting station 20 may and often is one of many collecting stations connected to the controller 10. Additional hub portions, each having such central collecting stations may be connected to the controller 10 such as indicated by means of additional main lines 26, 28 to form a group of hubs connected in parallel with the controller 10, the result being a complete loop system.
One of the difficulites that has occurred in such systems results from the fact that each hub portion, often containing as many as 15 modems, will be lost when a fault occurs in any one of the modems 14 or modem input or output lines 16, 18 since the series circuit connecting the group of modems 14 in the hub would then be open. Tracking down such a fault is an expensive and often time-consuming job during which time all of the modems 14 in the hub portion of the system are inoperative.
By means of my invention, this and other prior art difficulties often encountered in such transmission systems of the prior art are substantially overcome.